Cathode-ray oscillograph circuit



Patented Sept. 7. 1948 CATHODE-RAY ()SCILLOGRAPH CIRCUIT Peter S. Christaldi, Upper Montclair, N. J., as-

signor to Allen B. Du Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Application September 23, 1943, Serial No. 503,502

3 Claims.

This invention relates to a device for generating a controlling signal for use in connection with single sweep or repetitive time bases in a cathoderay oscillegraph. By this invention the beam intensity of an oscillograph can be controlled in such a manner that it is kept at zero intensity except during its forward trace.

In carrying out the invention a single sweep of the beam may be obtained from a circuit that normally yields a recurrent sawtooth wave. The controlling signal is used to turn on the beam just before it begins and to turn it off as soon as it has completed its forward trace.

The invention may be undersood from the description in connection with the accompanying drawing, in which:

Fig. l is a diagram of connections showing how the invention may be carried out;

Figs. 2 to are curves that will aid in explaining how the invention operates.

In the drawing, reference character l indicates a gas filled vacuum tube, to the grid of which a controlling signal is coupled from terminal 2 through capacitance 3, variable attenuator 4 and resistance in the cathode of tube l by means of the potential divider S and 3 connected to a source of positive potential. A source of positive potential is connected to the plate of tube i through resistance 5% and variable resistance 9. located between. this plate and cathode of tube I. The circuit so far described provides a sawtooth wave in the known way which can be synchronized by applying ignals at terminal 2.

A diode i? has its plate connected by lead 13 to the plate of tube i, and resistance i4 is located between the cathode of tube l2 and a point on potential divider 55, ii. A condenser i5 is connected between the lower end of this resistance id and ground. One end of resistance It is connected to a source of positive potential and the other end of this resistance is connected to a point between resistance i l and condenser l5. One end of resistance ll is connected to this point and the other end thereof is connected to ground.

A lead extends from the cathode of diode 2 to the grid of vacuum tube amplifier 2| which has its cathode biased by resistance 22. A positive potent-i is applied to the plate of tube 2! through resistance 23 in the usual way. This plate is coupled to resistances 25 and 26 in series. They are shown with condensers 2'! and 28, respectively, in parallel therewith. A lead 38 extends from points between resistances 25 and 26 and condensers 2i and 28 to the control grid 32 Operating grid bias 6 is provided A condenser Ill is .2 of cathode-ray tube 0. A source of negative potential, which may, for example, be minus-1500 volts, is connected to the lower end of the network -28 and to a voltage divider 34. The potential of the cathode 35 and first anode 36 of tube 0 are controlled by connections 31 and 38 to variable points on voltage divider 34, while one end of this voltage divider and the second anode 39 are connected to ground.

The operation is as follows:

It is obvious that if the diode l2 were disconnected a sawtooth signal would appear at the terminal G0 in the usual way. The frequency is controlled by resistances 8 and 9 and condenser ill, and can be synchronized within narrow limits by a synchronizing signal applied at 2. l

With this invention a single sweep can be obtained:

(1) By making the bias of diode [2 lower than the ionization potential of gas triode I and making the voltage drop across resistance 6 sufiiciently high;

(2) Or by keeping a fixed potential at the'oathode of tube l and decreasing the potential at the lower end of resistance l4;

(3) Or by adjusting the potential at both of these points so as to maintain the desired fixed range of potential on lead l3, thus maintaining a constant amplitude of the signal at terminal 40 to be used as the horizontal sweep for tube 0.

By this invention a signal is obtained from a recurrent sweep. This signal is used to turn on the beam of the tube 0' just before and during the interval of its horizontal sweep, the beam being extinguished the remainder of the time.

When the 400 v. potential is applied through resistances 8 and 9, the potential on the plates of tubes and I2 increases along the exponential curve i l of Fig. 2 until it reaches the level 4|, whereupon the diode l2 conducts, maintaining the potential at 4|, which is below the firing potential of gas triode I. When one of the synchronizing signals indicated at 42 in Fig. 3 reaches the rid of tube l, this tube conducts or fires and lowers the potential to the point 43, Fig. 2, at which the diode l2 ceases to conduct, whereupon the potential on the plates of tubes I and [2 rise along the line 44, Fig. 2, to the level 4| and. remains there until the next synchronizing signal is applied to the terminal 2. During this interval the current through diode l2 remains zero as shown at G5 in Fig. 4 and then rises abruptly to the line 45 when the diode begins to conduct, and remains there until the next synchronizing signal 42 arrives. During the interval 45 (Fig. 4) a rectangularly shaped pulse 47 of potential of negative polarity appears on the lead 29 that is connected to the cathode of the diode l2.

The pulse 41 on lead 20 is amplified and reversed in polarit by the amplifier 2|. The amplified pulse 41' is then applied in reversed positive polarity to the grid 32 after having been attenuated by the compensated resistance-capacitance attenuator 25-28, thus turnin the cathode-ray beam on at or just prior to the beginning of its forward trace and while it is accelerated by the first and second anodes 36 and 39 and is deflected by signals applied to the pairs of horizontal and vertical deflecting plates 49 and 50. The beam is cut off again at the end of the time interval represented by the line 41', Fig. 5.

The pulse 41, inverted and amplified in tube 2|, could be coupled to the grid 32 of cathoderay tube 0 in the usual way through a coupling condenser, with a resistor between grid 32 and the high-voltage source of negative potential. A disadvantage of this method is the difiiculty of maintaining uniform beam intensity, corresponding to freedom from slope of the pulse 41', when the interval of 41' is long. This difiiculty might be overcome by increasing the time constant of the coupling circuit, but this would often require the use of impractically large components because of the large difference in potentials of the two circuits.

By the present invention the coupling 25-28 is such that this difiiculty is overcome, and the advantages of direct coupling are obtained. It will be seen that by this invention the high D. C. negative potential at the grid 32 of tube 0 is attenuated in the resistances 25 and 23, while the amplified pulse signal appearing at the plate of tube 2| is attenuated inresistances 25 and 26, paralleled by condensers 21 and 28, and appears as 41' at the grid 32 of tube 0. It has been found that attenuations as low as 1 part in 5 are practicable in this arrangement.

Voltages and resistances represented on the drawing are illustrative.

What is claimed is:

1. In a device for increasing the intensity of the cathode-ray beam in the cathode-ra tube of an oscillograph during the application of a sweep deflection potential to said cathode-ray tube, 'means for generating a rectangularly shaped pulse of potential during the interval of said sweep potential, said means comprising a sawtooth signal generator, an electron discharge device of which the space current is made to vary between two predetermined values corresponding substantially to the extreme potentials of said sawtooth signal, said electron discharge device being connected to the output of said sawtooth signal generator, a load resistor connected to the output of said discharge device and across which said current generates said rectangularly shaped pulse of potential, and means for coupling said rectangularly shaped pulse of potential to a our- 4 rent-controlling electrode of said cathode-ray tube.

2. In a device for increasing the intensity of the cathode-ray beam in the cathode-ray tube of an oscillograph during the application of a sweep deflection potential to said cathode-ray tube, means for generating a rectangularly shaped pulse of potential during the interval of said sweep potential, said means comprising a sawtooth signal generator, an electron discharge device of which the space current is made to vary between two predetermined values corresponding substantially to the extreme potentials of said sawtooth signal, said electron discharge device being connected to the output of said sawtooth signal generator, a load resistor connected to the output of said discharge device and across which said current generates said rectangularly shaped pulse of potential, and means for coupling said rectangularly shaped pulse of potential to a current-controlling electrode of said cathode-ray tube said last named means comprising a resistive network compensated by capacitance to provide uniform frequency response.

3. The device of claim 1 in which said coupling means comprises a conductive three-terminal network, adapted to couple signals between two points having different potentials with respect to a third point, one terminal of said network being common to both input and output circuits, an input terminal to which signals are applied from the first one of said two points, an output terminal from which corresponding signals are taken and connected to the second one of said two points, said network having substantially uniform frequency transmission characteristics and being adapted for setting the potential which the output terminal assumes in the absence of 40 signals.

PETER S. CHRISTALDI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,622,851 Smith Mar. 29, 1927 2,059,004 Leeds Oct. 27, 1936 2,137,354 Schlesinger Nov. 22, 1938 2,179,111 Young Nov. 7, 1939 2,196,838 Rogowski et al. Apr. 9, 1940 2,210,702 Bowman-Manifold Aug. 6, 1940 2,222,943 George Nov. 26, 1940 2,230,926 Bingley Feb. 4, 1941 2,265,744 Rath Dec. 9, 1941 2,289,821 Boucke July 14, 1942 2,313,122 Brubaker Mar. 9, 1943 2,315,369 Foster Mar. 30, 1943 2,343,988 Mahoney Mar. 14, 1944 2,363,810 Schrader Nov. 28, 1944 2,369,138 Cook Feb. 13, 1945 

